/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase;

import static org.apache.hadoop.hbase.io.hfile.BlockType.MAGIC_LENGTH;

import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
import java.util.regex.Pattern;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * HConstants holds a bunch of HBase-related constants
 */
@InterfaceAudience.Public
public final class HConstants {
    // NOTICE!!!! Please do not add a constants here, unless they are referenced by a lot of classes.

    //Bytes.UTF8_ENCODING should be updated if this changed
    /** When we encode strings, we always specify UTF8 encoding */
    public static final String UTF8_ENCODING = "UTF-8";

    //Bytes.UTF8_CHARSET should be updated if this changed
    /** When we encode strings, we always specify UTF8 encoding */
    public static final Charset UTF8_CHARSET = Charset.forName(UTF8_ENCODING);
    /**
     * Default block size for an HFile.
     */
    public final static int DEFAULT_BLOCKSIZE = 64 * 1024;

    /** Used as a magic return value while optimized index key feature enabled(HBASE-7845) */
    public final static int INDEX_KEY_MAGIC = -2;
    /*
     * Name of directory that holds recovered edits written by the wal log
     * splitting code, one per region
     */
    public static final String RECOVERED_EDITS_DIR = "recovered.edits";
    /**
     * The first four bytes of Hadoop RPC connections
     */
    public static final byte[] RPC_HEADER = new byte[]{'H', 'B', 'a', 's'};
    public static final byte RPC_CURRENT_VERSION = 0;

    // HFileBlock constants. TODO!!!! THESE DEFINES BELONG IN HFILEBLOCK, NOT UP HERE.
    // Needed down in hbase-common though by encoders but these encoders should not be dealing
    // in the internals of hfileblocks. Fix encapsulation.

    /** The size data structures with minor version is 0 */
    public static final int HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM = MAGIC_LENGTH + 2 * Bytes.SIZEOF_INT + Bytes.SIZEOF_LONG;
    /** The size of a version 2 HFile block header, minor version 1.
     * There is a 1 byte checksum type, followed by a 4 byte bytesPerChecksum
     * followed by another 4 byte value to store sizeofDataOnDisk.
     */
    public static final int HFILEBLOCK_HEADER_SIZE = HFILEBLOCK_HEADER_SIZE_NO_CHECKSUM + Bytes.SIZEOF_BYTE + 2 * Bytes.SIZEOF_INT;
    /** Just an array of bytes of the right size. */
    public static final byte[] HFILEBLOCK_DUMMY_HEADER = new byte[HFILEBLOCK_HEADER_SIZE];

    //End HFileBlockConstants.

    /**
     * Status codes used for return values of bulk operations.
     */
    @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
    public enum OperationStatusCode {
        NOT_RUN, SUCCESS, BAD_FAMILY, STORE_TOO_BUSY, SANITY_CHECK_FAILURE, FAILURE
    }

    /** long constant for zero */
    public static final Long ZERO_L = Long.valueOf(0L);
    public static final String NINES = "99999999999999";
    public static final String ZEROES = "00000000000000";

    // For migration

    /** name of version file */
    public static final String VERSION_FILE_NAME = "hbase.version";

    /**
     * Current version of file system.
     * Version 4 supports only one kind of bloom filter.
     * Version 5 changes versions in catalog table regions.
     * Version 6 enables blockcaching on catalog tables.
     * Version 7 introduces hfile -- hbase 0.19 to 0.20..
     * Version 8 introduces namespace
     */
    // public static final String FILE_SYSTEM_VERSION = "6";
    public static final String FILE_SYSTEM_VERSION = "8";

    // Configuration parameters

    //TODO: Is having HBase homed on port 60k OK?

    /** Cluster is in distributed mode or not */
    public static final String CLUSTER_DISTRIBUTED = "hbase.cluster.distributed";

    /** Config for pluggable load balancers */
    public static final String HBASE_MASTER_LOADBALANCER_CLASS = "hbase.master.loadbalancer.class";

    /** Config for balancing the cluster by table */
    public static final String HBASE_MASTER_LOADBALANCE_BYTABLE = "hbase.master.loadbalance.bytable";

    /** Config for the max percent of regions in transition */
    public static final String HBASE_MASTER_BALANCER_MAX_RIT_PERCENT = "hbase.master.balancer.maxRitPercent";

    /** Default value for the max percent of regions in transition */
    public static final double DEFAULT_HBASE_MASTER_BALANCER_MAX_RIT_PERCENT = 1.0;

    /** Config for the max balancing time */
    public static final String HBASE_BALANCER_MAX_BALANCING = "hbase.balancer.max.balancing";

    /** Config for the balancer period */
    public static final String HBASE_BALANCER_PERIOD = "hbase.balancer.period";

    /** Default value for the balancer period */
    public static final int DEFAULT_HBASE_BALANCER_PERIOD = 300000;

    /** The name of the ensemble table */
    public static final TableName ENSEMBLE_TABLE_NAME = TableName.valueOf("hbase:ensemble");

    /** Config for pluggable region normalizer */
    public static final String HBASE_MASTER_NORMALIZER_CLASS = "hbase.master.normalizer.class";

    /** Cluster is standalone or pseudo-distributed */
    public static final boolean CLUSTER_IS_LOCAL = false;

    /** Cluster is fully-distributed */
    @Deprecated // unused. see HBASE-13636. remove this in 3.0
    public static final boolean CLUSTER_IS_DISTRIBUTED = true;

    /** Default value for cluster distributed mode */
    public static final boolean DEFAULT_CLUSTER_DISTRIBUTED = CLUSTER_IS_LOCAL;

    /** default host address */
    public static final String DEFAULT_HOST = "0.0.0.0";

    /** Parameter name for port master listens on. */
    public static final String MASTER_PORT = "hbase.master.port";

    /** default port that the master listens on */
    public static final int DEFAULT_MASTER_PORT = 16000;

    /** default port for master web api */
    public static final int DEFAULT_MASTER_INFOPORT = 16010;

    /** Configuration key for master web API port */
    public static final String MASTER_INFO_PORT = "hbase.master.info.port";

    /** Parameter name for the master type being backup (waits for primary to go inactive). */
    public static final String MASTER_TYPE_BACKUP = "hbase.master.backup";

    /**
     * by default every master is a possible primary master unless the conf explicitly overrides it
     * 默认情况下，每个主机都是可能的 active 主机，除非conf显式覆盖它
     */
    public static final boolean DEFAULT_MASTER_TYPE_BACKUP = false;

    /** Name of ZooKeeper quorum configuration parameter. */
    public static final String ZOOKEEPER_QUORUM = "hbase.zookeeper.quorum";

    /** Name of ZooKeeper quorum configuration parameter for client to locate meta. */
    public static final String CLIENT_ZOOKEEPER_QUORUM = "hbase.client.zookeeper.quorum";

    /** Client port of ZooKeeper for client to locate meta */
    public static final String CLIENT_ZOOKEEPER_CLIENT_PORT = "hbase.client.zookeeper.property.clientPort";

    /** Indicate whether the client ZK are observer nodes of the server ZK */
    public static final String CLIENT_ZOOKEEPER_OBSERVER_MODE = "hbase.client.zookeeper.observer.mode";
    /** Assuming client zk not in observer mode and master need to synchronize information */
    public static final boolean DEFAULT_CLIENT_ZOOKEEPER_OBSERVER_MODE = false;

    /** Common prefix of ZooKeeper configuration properties */
    public static final String ZK_CFG_PROPERTY_PREFIX = "hbase.zookeeper.property.";

    public static final int ZK_CFG_PROPERTY_PREFIX_LEN = ZK_CFG_PROPERTY_PREFIX.length();

    /**
     * The ZK client port key in the ZK properties map. The name reflects the
     * fact that this is not an HBase configuration key.
     */
    public static final String CLIENT_PORT_STR = "clientPort";

    /** Parameter name for the client port that the zookeeper listens on */
    public static final String ZOOKEEPER_CLIENT_PORT = ZK_CFG_PROPERTY_PREFIX + CLIENT_PORT_STR;

    /**
     * Will be removed in hbase 3.0
     * @deprecated use {@link #DEFAULT_ZOOKEEPER_CLIENT_PORT} instead
     */
    @Deprecated
    public static final int DEFAULT_ZOOKEPER_CLIENT_PORT = 2181;

    /** Default client port that the zookeeper listens on */
    public static final int DEFAULT_ZOOKEEPER_CLIENT_PORT = 2181;

    /**
     * Parameter name for the wait time for the recoverable zookeeper
     */
    @Deprecated // unused. see HBASE-3065. remove this in 3.0
    public static final String ZOOKEEPER_RECOVERABLE_WAITTIME = "hbase.zookeeper.recoverable.waittime";

    /** Default wait time for the recoverable zookeeper */
    @Deprecated // unused. see HBASE-3065. remove this in 3.0
    public static final long DEFAULT_ZOOKEPER_RECOVERABLE_WAITIME = 10000;

    /** Parameter name for the root dir in ZK for this cluster */
    public static final String ZOOKEEPER_ZNODE_PARENT = "zookeeper.znode.parent";

    /********
     * TODO_MA 马中华 https://blog.csdn.net/zhongqi2513
     *   注释： HBase 在 ZooKeeper 的默认根路径
     */
    public static final String DEFAULT_ZOOKEEPER_ZNODE_PARENT = "/hbase";

    /**
     * Parameter name for the limit on concurrent client-side zookeeper
     * connections
     */
    public static final String ZOOKEEPER_MAX_CLIENT_CNXNS = ZK_CFG_PROPERTY_PREFIX + "maxClientCnxns";

    /** Parameter name for the ZK data directory */
    public static final String ZOOKEEPER_DATA_DIR = ZK_CFG_PROPERTY_PREFIX + "dataDir";

    /** Parameter name for the ZK tick time */
    public static final String ZOOKEEPER_TICK_TIME = ZK_CFG_PROPERTY_PREFIX + "tickTime";

    /**
     * Will be removed in hbase 3.0
     * @deprecated use {@link #DEFAULT_ZOOKEEPER_MAX_CLIENT_CNXNS} instead
     */
    @Deprecated
    public static final int DEFAULT_ZOOKEPER_MAX_CLIENT_CNXNS = 300;

    /** Default limit on concurrent client-side zookeeper connections */
    public static final int DEFAULT_ZOOKEEPER_MAX_CLIENT_CNXNS = 300;

    /** Configuration key for ZooKeeper session timeout */
    public static final String ZK_SESSION_TIMEOUT = "zookeeper.session.timeout";

    /** Default value for ZooKeeper session timeout */
    public static final int DEFAULT_ZK_SESSION_TIMEOUT = 90 * 1000;

    /** Parameter name for port region server listens on. */
    public static final String REGIONSERVER_PORT = "hbase.regionserver.port";

    /** Default port region server listens on. */
    public static final int DEFAULT_REGIONSERVER_PORT = 16020;

    /** default port for region server web api */
    public static final int DEFAULT_REGIONSERVER_INFOPORT = 16030;

    /** A configuration key for regionserver info port */
    public static final String REGIONSERVER_INFO_PORT = "hbase.regionserver.info.port";

    /** A flag that enables automatic selection of regionserver info port */
    public static final String REGIONSERVER_INFO_PORT_AUTO = REGIONSERVER_INFO_PORT + ".auto";

    /** Parameter name for what region server implementation to use. */
    public static final String REGION_SERVER_IMPL = "hbase.regionserver.impl";

    /** Parameter name for what master implementation to use. */
    public static final String MASTER_IMPL = "hbase.master.impl";

    /** Parameter name for what hbase client implementation to use. */
    @Deprecated // unused. see HBASE-7460. remove this in 3.0
    public static final String HBASECLIENT_IMPL = "hbase.hbaseclient.impl";

    /** Parameter name for how often threads should wake up */
    public static final String THREAD_WAKE_FREQUENCY = "hbase.server.thread.wakefrequency";

    /** Default value for thread wake frequency */
    public static final int DEFAULT_THREAD_WAKE_FREQUENCY = 10 * 1000;

    /** Parameter name for how often we should try to write a version file, before failing */
    public static final String VERSION_FILE_WRITE_ATTEMPTS = "hbase.server.versionfile.writeattempts";

    /** Parameter name for how often we should try to write a version file, before failing */
    public static final int DEFAULT_VERSION_FILE_WRITE_ATTEMPTS = 3;

    /** Parameter name and default value for how often a region should perform a major compaction */
    public static final String MAJOR_COMPACTION_PERIOD = "hbase.hregion.majorcompaction";
    public static final long DEFAULT_MAJOR_COMPACTION_PERIOD = 1000 * 60 * 60 * 24 * 7; // 7 days

    /**
     * Parameter name and default value for major compaction jitter.
     * Used as a multiplier applied to {@link HConstants#MAJOR_COMPACTION_PERIOD}
     * to cause compaction to occur a given amount of time either side of
     * {@link HConstants#MAJOR_COMPACTION_PERIOD}.
     * Default to 0.5 so jitter has us fall evenly either side of when the compaction should run.
     */
    public static final String MAJOR_COMPACTION_JITTER = "hbase.hregion.majorcompaction.jitter";
    public static final float DEFAULT_MAJOR_COMPACTION_JITTER = 0.50F;

    /** Parameter name for the maximum batch of KVs to be used in flushes and compactions */
    public static final String COMPACTION_KV_MAX = "hbase.hstore.compaction.kv.max";
    public static final int COMPACTION_KV_MAX_DEFAULT = 10;

    /** Parameter name for HBase instance root directory */
    public static final String HBASE_DIR = "hbase.rootdir";

    /** Parameter name for HBase client IPC pool type */
    public static final String HBASE_CLIENT_IPC_POOL_TYPE = "hbase.client.ipc.pool.type";

    /** Parameter name for HBase client IPC pool size */
    public static final String HBASE_CLIENT_IPC_POOL_SIZE = "hbase.client.ipc.pool.size";

    /** Parameter name for HBase client operation timeout. */
    public static final String HBASE_CLIENT_OPERATION_TIMEOUT = "hbase.client.operation.timeout";

    /** Parameter name for HBase client meta operation timeout. */
    public static final String HBASE_CLIENT_META_OPERATION_TIMEOUT = "hbase.client.meta.operation.timeout";

    /** Default HBase client operation timeout, which is tantamount to a blocking call */
    public static final int DEFAULT_HBASE_CLIENT_OPERATION_TIMEOUT = 1200000;

    /** Parameter name for HBase client meta replica scan call timeout. */
    public static final String HBASE_CLIENT_META_REPLICA_SCAN_TIMEOUT = "hbase.client.meta.replica.scan.timeout";

    /** Default HBase client meta replica scan call timeout, 1 second */
    public static final int HBASE_CLIENT_META_REPLICA_SCAN_TIMEOUT_DEFAULT = 1000000;

    /** Used to construct the name of the log directory for a region server */
    public static final String HREGION_LOGDIR_NAME = "WALs";

    /** Used to construct the name of the splitlog directory for a region server */
    public static final String SPLIT_LOGDIR_NAME = "splitWAL";

    /** Like the previous, but for old logs that are about to be deleted */
    public static final String HREGION_OLDLOGDIR_NAME = "oldWALs";

    /** Staging dir used by bulk load */
    public static final String BULKLOAD_STAGING_DIR_NAME = "staging";

    public static final String CORRUPT_DIR_NAME = "corrupt";

    /** Used by HBCK to sideline backup data */
    public static final String HBCK_SIDELINEDIR_NAME = ".hbck";

    /** Any artifacts left from migration can be moved here */
    public static final String MIGRATION_NAME = ".migration";

    /**
     * The directory from which co-processor/custom filter jars can be loaded
     * dynamically by the region servers. This value can be overridden by the
     * hbase.dynamic.jars.dir config.
     */
    @Deprecated // unused. see HBASE-12054. remove this in 3.0
    public static final String LIB_DIR = "lib";

    /** Used to construct the name of the compaction directory during compaction */
    public static final String HREGION_COMPACTIONDIR_NAME = "compaction.dir";

    /** Conf key for the max file size after which we split the region */
    public static final String HREGION_MAX_FILESIZE = "hbase.hregion.max.filesize";

    /** Default maximum file size */
    public static final long DEFAULT_MAX_FILE_SIZE = 10 * 1024 * 1024 * 1024L;

    /**
     * Max size of single row for Get's or Scan's without in-row scanning flag set.
     */
    public static final String TABLE_MAX_ROWSIZE_KEY = "hbase.table.max.rowsize";

    /**
     * Default max row size (1 Gb).
     */
    public static final long TABLE_MAX_ROWSIZE_DEFAULT = 1024 * 1024 * 1024L;

    /**
     * The max number of threads used for opening and closing stores or store
     * files in parallel
     */
    public static final String HSTORE_OPEN_AND_CLOSE_THREADS_MAX = "hbase.hstore.open.and.close.threads.max";

    /**
     * The default number for the max number of threads used for opening and
     * closing stores or store files in parallel
     */
    public static final int DEFAULT_HSTORE_OPEN_AND_CLOSE_THREADS_MAX = 1;

    /**
     * Block updates if memstore has hbase.hregion.memstore.block.multiplier
     * times hbase.hregion.memstore.flush.size bytes.  Useful preventing
     * runaway memstore during spikes in update traffic.
     */
    public static final String HREGION_MEMSTORE_BLOCK_MULTIPLIER = "hbase.hregion.memstore.block.multiplier";

    /**
     * Default value for hbase.hregion.memstore.block.multiplier
     */
    public static final int DEFAULT_HREGION_MEMSTORE_BLOCK_MULTIPLIER = 4;

    /** Conf key for the memstore size at which we flush the memstore */
    public static final String HREGION_MEMSTORE_FLUSH_SIZE = "hbase.hregion.memstore.flush.size";

    public static final String HREGION_EDITS_REPLAY_SKIP_ERRORS = "hbase.hregion.edits.replay.skip.errors";

    public static final boolean DEFAULT_HREGION_EDITS_REPLAY_SKIP_ERRORS = false;

    /** Maximum value length, enforced on KeyValue construction */
    public static final int MAXIMUM_VALUE_LENGTH = Integer.MAX_VALUE - 1;

    /** name of the file for unique cluster ID */
    public static final String CLUSTER_ID_FILE_NAME = "hbase.id";

    /** Default value for cluster ID */
    public static final String CLUSTER_ID_DEFAULT = "default-cluster";

    /** Parameter name for # days to keep MVCC values during a major compaction */
    public static final String KEEP_SEQID_PERIOD = "hbase.hstore.compaction.keep.seqId.period";
    /** At least to keep MVCC values in hfiles for 5 days */
    public static final int MIN_KEEP_SEQID_PERIOD = 5;

    // Always store the location of the root table's HRegion.
    // This HRegion is never split.

    // region name = table + startkey + regionid. This is the row key.
    // each row in the root and meta tables describes exactly 1 region
    // Do we ever need to know all the information that we are storing?

    // Note that the name of the root table starts with "-" and the name of the
    // meta table starts with "." Why? it's a trick. It turns out that when we
    // store region names in memory, we use a SortedMap. Since "-" sorts before
    // "." (and since no other table name can start with either of these
    // characters, the root region will always be the first entry in such a Map,
    // followed by all the meta regions (which will be ordered by their starting
    // row key as well), followed by all user tables. So when the Master is
    // choosing regions to assign, it will always choose the root region first,
    // followed by the meta regions, followed by user regions. Since the root
    // and meta regions always need to be on-line, this ensures that they will
    // be the first to be reassigned if the server(s) they are being served by
    // should go down.

    public static final String BASE_NAMESPACE_DIR = "data";

    /** delimiter used between portions of a region name */
    public static final int META_ROW_DELIMITER = ',';

    /** The catalog family as a string*/
    public static final String CATALOG_FAMILY_STR = "info";

    /** The catalog family */
    public static final byte[] CATALOG_FAMILY = Bytes.toBytes(CATALOG_FAMILY_STR);

    /** The RegionInfo qualifier as a string */
    public static final String REGIONINFO_QUALIFIER_STR = "regioninfo";

    /** The regioninfo column qualifier */
    public static final byte[] REGIONINFO_QUALIFIER = Bytes.toBytes(REGIONINFO_QUALIFIER_STR);

    /** The server column qualifier */
    public static final String SERVER_QUALIFIER_STR = "server";
    /** The server column qualifier */
    public static final byte[] SERVER_QUALIFIER = Bytes.toBytes(SERVER_QUALIFIER_STR);

    /** The startcode column qualifier */
    public static final String STARTCODE_QUALIFIER_STR = "serverstartcode";
    /** The startcode column qualifier */
    public static final byte[] STARTCODE_QUALIFIER = Bytes.toBytes(STARTCODE_QUALIFIER_STR);

    /** The open seqnum column qualifier */
    public static final String SEQNUM_QUALIFIER_STR = "seqnumDuringOpen";
    /** The open seqnum column qualifier */
    public static final byte[] SEQNUM_QUALIFIER = Bytes.toBytes(SEQNUM_QUALIFIER_STR);

    /** The state column qualifier */
    public static final String STATE_QUALIFIER_STR = "state";

    public static final byte[] STATE_QUALIFIER = Bytes.toBytes(STATE_QUALIFIER_STR);

    /**
     * The serverName column qualifier. Its the server where the region is
     * transitioning on, while column server is the server where the region is
     * opened on. They are the same when the region is in state OPEN.
     */
    public static final String SERVERNAME_QUALIFIER_STR = "sn";

    public static final byte[] SERVERNAME_QUALIFIER = Bytes.toBytes(SERVERNAME_QUALIFIER_STR);

    /** The lower-half split region column qualifier */
    public static final byte[] SPLITA_QUALIFIER = Bytes.toBytes("splitA");

    /** The upper-half split region column qualifier */
    public static final byte[] SPLITB_QUALIFIER = Bytes.toBytes("splitB");

    /**
     * Merge qualifier prefix.
     * We used to only allow two regions merge; mergeA and mergeB.
     * Now we allow many to merge. Each region to merge will be referenced
     * in a column whose qualifier starts with this define.
     */
    public static final String MERGE_QUALIFIER_PREFIX_STR = "merge";
    public static final byte[] MERGE_QUALIFIER_PREFIX = Bytes.toBytes(MERGE_QUALIFIER_PREFIX_STR);

    /**
     * The lower-half merge region column qualifier
     * @deprecated Since 2.3.0 and 2.2.1. Not used anymore. Instead we look for
     *   the {@link #MERGE_QUALIFIER_PREFIX_STR} prefix.
     */
    @Deprecated
    public static final byte[] MERGEA_QUALIFIER = Bytes.toBytes(MERGE_QUALIFIER_PREFIX_STR + "A");

    /**
     * The upper-half merge region column qualifier
     * @deprecated Since 2.3.0 and 2.2.1. Not used anymore. Instead we look for
     *   the {@link #MERGE_QUALIFIER_PREFIX_STR} prefix.
     */
    @Deprecated
    public static final byte[] MERGEB_QUALIFIER = Bytes.toBytes(MERGE_QUALIFIER_PREFIX_STR + "B");

    /** The catalog family as a string*/
    public static final String TABLE_FAMILY_STR = "table";

    /** The catalog family */
    public static final byte[] TABLE_FAMILY = Bytes.toBytes(TABLE_FAMILY_STR);

    /** The serialized table state qualifier */
    public static final byte[] TABLE_STATE_QUALIFIER = Bytes.toBytes("state");

    /** The replication barrier family as a string*/
    public static final String REPLICATION_BARRIER_FAMILY_STR = "rep_barrier";

    /** The replication barrier family */
    public static final byte[] REPLICATION_BARRIER_FAMILY = Bytes.toBytes(REPLICATION_BARRIER_FAMILY_STR);

    /**
     * The meta table version column qualifier.
     * We keep current version of the meta table in this column in <code>-ROOT-</code>
     * table: i.e. in the 'info:v' column.
     */
    public static final byte[] META_VERSION_QUALIFIER = Bytes.toBytes("v");

    /**
     * The current version of the meta table.
     * - pre-hbase 0.92.  There is no META_VERSION column in the root table
     * in this case. The meta has HTableDescriptor serialized into the HRegionInfo;
     * - version 0 is 0.92 and 0.94. Meta data has serialized HRegionInfo's using
     * Writable serialization, and HRegionInfo's does not contain HTableDescriptors.
     * - version 1 for 0.96+ keeps HRegionInfo data structures, but changes the
     * byte[] serialization from Writables to Protobuf.
     * See HRegionInfo.VERSION
     */
    public static final short META_VERSION = 1;

    // Other constants

    /**
     * An empty byte array instance.
     */
    public static final byte[] EMPTY_BYTE_ARRAY = new byte[0];

    /**
     * An empty string instance.
     */
    public static final String EMPTY_STRING = "";

    public static final ByteBuffer EMPTY_BYTE_BUFFER = ByteBuffer.wrap(EMPTY_BYTE_ARRAY);

    /**
     * Used by scanners, etc when they want to start at the beginning of a region
     */
    public static final byte[] EMPTY_START_ROW = EMPTY_BYTE_ARRAY;

    /**
     * Last row in a table.
     */
    public static final byte[] EMPTY_END_ROW = EMPTY_START_ROW;

    /**
     * Used by scanners and others when they're trying to detect the end of a
     * table
     */
    public static final byte[] LAST_ROW = EMPTY_BYTE_ARRAY;

    /**
     * Max length a row can have because of the limitation in TFile.
     */
    public static final int MAX_ROW_LENGTH = Short.MAX_VALUE;

    /**
     * Timestamp to use when we want to refer to the latest cell.
     * This is the timestamp sent by clients when no timestamp is specified on
     * commit.
     */
    public static final long LATEST_TIMESTAMP = Long.MAX_VALUE;

    /**
     * Timestamp to use when we want to refer to the oldest cell.
     * Special! Used in fake Cells only. Should never be the timestamp on an actual Cell returned to
     * a client.
     * @deprecated Should not be public since hbase-1.3.0. For internal use only. Move internal to
     *   Scanners flagged as special timestamp value never to be returned as timestamp on a Cell.
     */
    @Deprecated
    public static final long OLDEST_TIMESTAMP = Long.MIN_VALUE;

    /**
     * LATEST_TIMESTAMP in bytes form
     */
    public static final byte[] LATEST_TIMESTAMP_BYTES = {
            // big-endian
            (byte) (LATEST_TIMESTAMP >>> 56), (byte) (LATEST_TIMESTAMP >>> 48), (byte) (LATEST_TIMESTAMP >>> 40), (byte) (LATEST_TIMESTAMP >>> 32), (byte) (LATEST_TIMESTAMP >>> 24), (byte) (LATEST_TIMESTAMP >>> 16), (byte) (LATEST_TIMESTAMP >>> 8), (byte) LATEST_TIMESTAMP,};

    /**
     * Define for 'return-all-versions'.
     */
    public static final int ALL_VERSIONS = Integer.MAX_VALUE;

    /**
     * Unlimited time-to-live.
     */
    //  public static final int FOREVER = -1;
    public static final int FOREVER = Integer.MAX_VALUE;

    /**
     * Seconds in a week
     */
    @Deprecated // unused. see HBASE-2692. remove this in 3.0
    public static final int WEEK_IN_SECONDS = 7 * 24 * 3600;

    /**
     * Seconds in a day, hour and minute
     */
    public static final int DAY_IN_SECONDS = 24 * 60 * 60;
    public static final int HOUR_IN_SECONDS = 60 * 60;
    public static final int MINUTE_IN_SECONDS = 60;

    //TODO: although the following are referenced widely to format strings for
    //      the shell. They really aren't a part of the public API. It would be
    //      nice if we could put them somewhere where they did not need to be
    //      public. They could have package visibility
    public static final String NAME = "NAME";
    public static final String VERSIONS = "VERSIONS";
    public static final String IN_MEMORY = "IN_MEMORY";
    public static final String METADATA = "METADATA";
    public static final String CONFIGURATION = "CONFIGURATION";

    /**
     * Retrying we multiply hbase.client.pause setting by what we have in this array until we
     * run out of array items.  Retries beyond this use the last number in the array.  So, for
     * example, if hbase.client.pause is 1 second, and maximum retries count
     * hbase.client.retries.number is 10, we will retry at the following intervals:
     * 1, 2, 3, 5, 10, 20, 40, 100, 100, 100.
     * With 100ms, a back-off of 200 means 20s
     */
    public static final int[] RETRY_BACKOFF = {1, 2, 3, 5, 10, 20, 40, 100, 100, 100, 100, 200, 200};

    public static final String REGION_IMPL = "hbase.hregion.impl";

    /**
     * Scope tag for locally scoped data.
     * This data will not be replicated.
     */
    public static final int REPLICATION_SCOPE_LOCAL = 0;

    /**
     * Scope tag for globally scoped data.
     * This data will be replicated to all peers.
     */
    public static final int REPLICATION_SCOPE_GLOBAL = 1;

    /**
     * Default cluster ID, cannot be used to identify a cluster so a key with
     * this value means it wasn't meant for replication.
     */
    public static final UUID DEFAULT_CLUSTER_ID = new UUID(0L, 0L);

    /**
     * Parameter name for maximum number of bytes returned when calling a scanner's next method.
     * Controlled by the client.
     */
    public static final String HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE_KEY = "hbase.client.scanner.max.result.size";

    /**
     * Parameter name for maximum number of bytes returned when calling a scanner's next method.
     * Controlled by the server.
     */
    public static final String HBASE_SERVER_SCANNER_MAX_RESULT_SIZE_KEY = "hbase.server.scanner.max.result.size";

    /**
     * Maximum number of bytes returned when calling a scanner's next method.
     * Note that when a single row is larger than this limit the row is still
     * returned completely.
     *
     * The default value is 2MB.
     */
    public static final long DEFAULT_HBASE_CLIENT_SCANNER_MAX_RESULT_SIZE = 2 * 1024 * 1024;

    /**
     * Maximum number of bytes returned when calling a scanner's next method.
     * Note that when a single row is larger than this limit the row is still
     * returned completely.
     * Safety setting to protect the region server.
     *
     * The default value is 100MB. (a client would rarely request larger chunks on purpose)
     */
    public static final long DEFAULT_HBASE_SERVER_SCANNER_MAX_RESULT_SIZE = 100 * 1024 * 1024;

    /**
     * Parameter name for client pause value, used mostly as value to wait
     * before running a retry of a failed get, region lookup, etc.
     */
    public static final String HBASE_CLIENT_PAUSE = "hbase.client.pause";

    /**
     * Default value of {@link #HBASE_CLIENT_PAUSE}.
     */
    public static final long DEFAULT_HBASE_CLIENT_PAUSE = 100;

    /**
     * Parameter name for client pause value for special case such as call queue too big, etc.
     */
    public static final String HBASE_CLIENT_PAUSE_FOR_CQTBE = "hbase.client.pause.cqtbe";

    /**
     * The maximum number of concurrent connections the client will maintain.
     */
    public static final String HBASE_CLIENT_MAX_TOTAL_TASKS = "hbase.client.max.total.tasks";

    /**
     * Default value of {@link #HBASE_CLIENT_MAX_TOTAL_TASKS}.
     */
    public static final int DEFAULT_HBASE_CLIENT_MAX_TOTAL_TASKS = 100;

    /**
     * The maximum number of concurrent connections the client will maintain to a single
     * RegionServer.
     */
    public static final String HBASE_CLIENT_MAX_PERSERVER_TASKS = "hbase.client.max.perserver.tasks";

    /**
     * Default value of {@link #HBASE_CLIENT_MAX_PERSERVER_TASKS}.
     */
    public static final int DEFAULT_HBASE_CLIENT_MAX_PERSERVER_TASKS = 2;

    /**
     * The maximum number of concurrent connections the client will maintain to a single
     * Region.
     */
    public static final String HBASE_CLIENT_MAX_PERREGION_TASKS = "hbase.client.max.perregion.tasks";

    /**
     * Default value of {@link #HBASE_CLIENT_MAX_PERREGION_TASKS}.
     */
    public static final int DEFAULT_HBASE_CLIENT_MAX_PERREGION_TASKS = 1;

    /**
     * The maximum number of concurrent pending RPC requests for one server in process level.
     */
    public static final String HBASE_CLIENT_PERSERVER_REQUESTS_THRESHOLD = "hbase.client.perserver.requests.threshold";

    /**
     * Default value of {@link #HBASE_CLIENT_PERSERVER_REQUESTS_THRESHOLD}.
     */
    public static final int DEFAULT_HBASE_CLIENT_PERSERVER_REQUESTS_THRESHOLD = Integer.MAX_VALUE;


    /**
     * Parameter name for server pause value, used mostly as value to wait before
     * running a retry of a failed operation.
     */
    public static final String HBASE_SERVER_PAUSE = "hbase.server.pause";

    /**
     * Default value of {@link #HBASE_SERVER_PAUSE}.
     */
    public static final int DEFAULT_HBASE_SERVER_PAUSE = 1000;

    /**
     * Parameter name for maximum retries, used as maximum for all retryable
     * operations such as fetching of the root region from root region server,
     * getting a cell's value, starting a row update, etc.
     */
    public static final String HBASE_CLIENT_RETRIES_NUMBER = "hbase.client.retries.number";

    /**
     * Default value of {@link #HBASE_CLIENT_RETRIES_NUMBER}.
     */
    public static final int DEFAULT_HBASE_CLIENT_RETRIES_NUMBER = 15;

    public static final String HBASE_CLIENT_SERVERSIDE_RETRIES_MULTIPLIER = "hbase.client.serverside.retries.multiplier";

    public static final int DEFAULT_HBASE_CLIENT_SERVERSIDE_RETRIES_MULTIPLIER = 3;

    /**
     * Parameter name to set the default scanner caching for all clients.
     */
    public static final String HBASE_CLIENT_SCANNER_CACHING = "hbase.client.scanner.caching";

    /**
     * Default value for {@link #HBASE_CLIENT_SCANNER_CACHING}
     */
    public static final int DEFAULT_HBASE_CLIENT_SCANNER_CACHING = Integer.MAX_VALUE;

    /**
     * Parameter name for number of rows that will be fetched when calling next on
     * a scanner if it is not served from memory. Higher caching values will
     * enable faster scanners but will eat up more memory and some calls of next
     * may take longer and longer times when the cache is empty.
     */
    public static final String HBASE_META_SCANNER_CACHING = "hbase.meta.scanner.caching";

    /**
     * Default value of {@link #HBASE_META_SCANNER_CACHING}.
     */
    public static final int DEFAULT_HBASE_META_SCANNER_CACHING = 100;

    /**
     * Parameter name for number of versions, kept by meta table.
     */
    public static final String HBASE_META_VERSIONS = "hbase.meta.versions";

    /**
     * Default value of {@link #HBASE_META_VERSIONS}.
     */
    public static final int DEFAULT_HBASE_META_VERSIONS = 3;

    /**
     * Parameter name for number of versions, kept by meta table.
     */
    public static final String HBASE_META_BLOCK_SIZE = "hbase.meta.blocksize";

    /**
     * Default value of {@link #HBASE_META_BLOCK_SIZE}.
     */
    public static final int DEFAULT_HBASE_META_BLOCK_SIZE = 8 * 1024;

    /**
     * Parameter name for unique identifier for this {@link org.apache.hadoop.conf.Configuration}
     * instance. If there are two or more {@link org.apache.hadoop.conf.Configuration} instances that,
     * for all intents and purposes, are the same except for their instance ids, then they will not be
     * able to share the same org.apache.hadoop.hbase.client.HConnection instance. On the other hand,
     * even if the instance ids are the same, it could result in non-shared
     * org.apache.hadoop.hbase.client.HConnection instances if some of the other connection parameters
     * differ.
     */
    public static final String HBASE_CLIENT_INSTANCE_ID = "hbase.client.instance.id";

    /**
     * The client scanner timeout period in milliseconds.
     */
    public static final String HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD = "hbase.client.scanner.timeout.period";

    /**
     * Use {@link #HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD} instead.
     * @deprecated This config option is deprecated. Will be removed at later releases after 0.96.
     */
    @Deprecated
    public static final String HBASE_REGIONSERVER_LEASE_PERIOD_KEY = "hbase.regionserver.lease.period";

    /**
     * Default value of {@link #HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD}.
     */
    public static final int DEFAULT_HBASE_CLIENT_SCANNER_TIMEOUT_PERIOD = 60000;

    /**
     * timeout for each RPC
     */
    public static final String HBASE_RPC_TIMEOUT_KEY = "hbase.rpc.timeout";

    /**
     * timeout for each read RPC
     */
    public static final String HBASE_RPC_READ_TIMEOUT_KEY = "hbase.rpc.read.timeout";

    /**
     * timeout for each write RPC
     */
    public static final String HBASE_RPC_WRITE_TIMEOUT_KEY = "hbase.rpc.write.timeout";

    /**
     * Default value of {@link #HBASE_RPC_TIMEOUT_KEY}
     */
    public static final int DEFAULT_HBASE_RPC_TIMEOUT = 60000;

    /**
     * timeout for short operation RPC
     */
    public static final String HBASE_RPC_SHORTOPERATION_TIMEOUT_KEY = "hbase.rpc.shortoperation.timeout";

    /**
     * Default value of {@link #HBASE_RPC_SHORTOPERATION_TIMEOUT_KEY}
     */
    public static final int DEFAULT_HBASE_RPC_SHORTOPERATION_TIMEOUT = 10000;

    /**
     * Value indicating the server name was saved with no sequence number.
     */
    public static final long NO_SEQNUM = -1;


    /*
     * cluster replication constants.
     */
    public static final String REPLICATION_SOURCE_SERVICE_CLASSNAME = "hbase.replication.source.service";
    public static final String REPLICATION_SINK_SERVICE_CLASSNAME = "hbase.replication.sink.service";
    public static final String REPLICATION_SERVICE_CLASSNAME_DEFAULT = "org.apache.hadoop.hbase.replication.regionserver.Replication";
    public static final String REPLICATION_BULKLOAD_ENABLE_KEY = "hbase.replication.bulkload.enabled";
    public static final boolean REPLICATION_BULKLOAD_ENABLE_DEFAULT = false;
    /** Replication cluster id of source cluster which uniquely identifies itself with peer cluster */
    public static final String REPLICATION_CLUSTER_ID = "hbase.replication.cluster.id";
    /**
     * Max total size of buffered entries in all replication peers. It will prevent server getting
     * OOM if there are many peers. Default value is 256MB which is four times to default
     * replication.source.size.capacity.
     */
    public static final String REPLICATION_SOURCE_TOTAL_BUFFER_KEY = "replication.total.buffer.quota";

    public static final int REPLICATION_SOURCE_TOTAL_BUFFER_DFAULT = 256 * 1024 * 1024;

    /** Configuration key for ReplicationSource shipeEdits timeout */
    public static final String REPLICATION_SOURCE_SHIPEDITS_TIMEOUT = "replication.source.shipedits.timeout";
    public static final int REPLICATION_SOURCE_SHIPEDITS_TIMEOUT_DFAULT = 60000;

    /**
     * Directory where the source cluster file system client configuration are placed which is used by
     * sink cluster to copy HFiles from source cluster file system
     */
    public static final String REPLICATION_CONF_DIR = "hbase.replication.conf.dir";

    /** Maximum time to retry for a failed bulk load request */
    public static final String BULKLOAD_MAX_RETRIES_NUMBER = "hbase.bulkload.retries.number";

    /** HBCK special code name used as server name when manipulating ZK nodes */
    @Deprecated // unused. see HBASE-3789. remove this in 3.0
    public static final String HBCK_CODE_NAME = "HBCKServerName";

    public static final String KEY_FOR_HOSTNAME_SEEN_BY_MASTER = "hbase.regionserver.hostname.seen.by.master";

    public static final String HBASE_MASTER_LOGCLEANER_PLUGINS = "hbase.master.logcleaner.plugins";

    public static final String HBASE_REGION_SPLIT_POLICY_KEY = "hbase.regionserver.region.split.policy";

    /** Whether nonces are enabled; default is true. */
    public static final String HBASE_RS_NONCES_ENABLED = "hbase.regionserver.nonces.enabled";

    /**
     * Configuration key for the size of the block cache
     */
    public static final String HFILE_BLOCK_CACHE_SIZE_KEY = "hfile.block.cache.size";

    public static final float HFILE_BLOCK_CACHE_SIZE_DEFAULT = 0.4f;

    /*
     * Minimum percentage of free heap necessary for a successful cluster startup.
     */
    public static final float HBASE_CLUSTER_MINIMUM_MEMORY_THRESHOLD = 0.2f;

    /**
     * @deprecated It is used internally. As of release 2.0.0, this will be removed in HBase 3.0.0.
     */
    @Deprecated
    public static final Pattern CP_HTD_ATTR_KEY_PATTERN = Pattern.compile("^coprocessor\\$([0-9]+)$", Pattern.CASE_INSENSITIVE);

    /**
     * <pre>
     * Pattern that matches a coprocessor specification. Form is:
     * {@code <coprocessor jar file location> '|' <class name> ['|' <priority> ['|' <arguments>]]}
     * where arguments are {@code <KEY> '=' <VALUE> [,...]}
     * For example: {@code hdfs:///foo.jar|com.foo.FooRegionObserver|1001|arg1=1,arg2=2}
     * </pre>
     * @deprecated It is used internally. As of release 2.0.0, this will be removed in HBase 3.0.0.
     */
    @Deprecated
    public static final Pattern CP_HTD_ATTR_VALUE_PATTERN = Pattern.compile("(^[^\\|]*)\\|([^\\|]+)\\|[\\s]*([\\d]*)[\\s]*(\\|.*)?$");
    /**
     * @deprecated It is used internally. As of release 2.0.0, this will be removed in HBase 3.0.0.
     */
    @Deprecated
    public static final String CP_HTD_ATTR_VALUE_PARAM_KEY_PATTERN = "[^=,]+";
    /**
     * @deprecated It is used internally. As of release 2.0.0, this will be removed in HBase 3.0.0.
     */
    @Deprecated
    public static final String CP_HTD_ATTR_VALUE_PARAM_VALUE_PATTERN = "[^,]+";
    /**
     * @deprecated It is used internally. As of release 2.0.0, this will be removed in HBase 3.0.0.
     */
    @Deprecated
    public static final Pattern CP_HTD_ATTR_VALUE_PARAM_PATTERN = Pattern
            .compile("(" + CP_HTD_ATTR_VALUE_PARAM_KEY_PATTERN + ")=(" + CP_HTD_ATTR_VALUE_PARAM_VALUE_PATTERN + "),?");
    public static final String CP_HTD_ATTR_INCLUSION_KEY = "hbase.coprocessor.classloader.included.classes";

    /** The delay when re-trying a socket operation in a loop (HBASE-4712) */
    public static final int SOCKET_RETRY_WAIT_MS = 200;

    /** Host name of the local machine */
    public static final String LOCALHOST = "localhost";

    /**
     * If this parameter is set to true, then hbase will read
     * data and then verify checksums. Checksum verification
     * inside hdfs will be switched off.  However, if the hbase-checksum
     * verification fails, then it will switch back to using
     * hdfs checksums for verifiying data that is being read from storage.
     *
     * If this parameter is set to false, then hbase will not
     * verify any checksums, instead it will depend on checksum verification
     * being done in the hdfs client.
     */
    public static final String HBASE_CHECKSUM_VERIFICATION = "hbase.regionserver.checksum.verify";

    public static final String LOCALHOST_IP = "127.0.0.1";

    public static final String REGION_SERVER_HANDLER_COUNT = "hbase.regionserver.handler.count";
    public static final int DEFAULT_REGION_SERVER_HANDLER_COUNT = 30;

    /*
     * REGION_SERVER_HANDLER_ABORT_ON_ERROR_PERCENT:
     * -1  => Disable aborting
     * 0   => Abort if even a single handler has died
     * 0.x => Abort only when this percent of handlers have died
     * 1   => Abort only all of the handers have died
     */
    public static final String REGION_SERVER_HANDLER_ABORT_ON_ERROR_PERCENT = "hbase.regionserver.handler.abort.on.error.percent";
    public static final double DEFAULT_REGION_SERVER_HANDLER_ABORT_ON_ERROR_PERCENT = 0.5;

    //High priority handlers to deal with admin requests and system table operation requests
    public static final String REGION_SERVER_HIGH_PRIORITY_HANDLER_COUNT = "hbase.regionserver.metahandler.count";
    public static final int DEFAULT_REGION_SERVER_HIGH_PRIORITY_HANDLER_COUNT = 20;

    public static final String REGION_SERVER_REPLICATION_HANDLER_COUNT = "hbase.regionserver.replication.handler.count";
    public static final int DEFAULT_REGION_SERVER_REPLICATION_HANDLER_COUNT = 3;
    // Meta Transition handlers to deal with meta ReportRegionStateTransitionRequest. Meta transition
    // should be dealt with in a separate handler in case blocking other region's transition.
    public static final String MASTER_META_TRANSITION_HANDLER_COUNT = "hbase.master.meta.transition.handler.count";
    public static final int MASTER__META_TRANSITION_HANDLER_COUNT_DEFAULT = 1;

    @Deprecated // unused. see HBASE-10569. remove this in 3.0
    public static final String MASTER_HANDLER_COUNT = "hbase.master.handler.count";
    @Deprecated // unused. see HBASE-10569. remove this in 3.0
    public static final int DEFAULT_MASTER_HANLDER_COUNT = 25;

    /** Conf key that specifies timeout value to wait for a region ready */
    @Deprecated // unused. see HBASE-13616. remove this in 3.0
    public static final String LOG_REPLAY_WAIT_REGION_TIMEOUT = "hbase.master.log.replay.wait.region.timeout";

    /** Conf key for enabling meta replication */
    public static final String USE_META_REPLICAS = "hbase.meta.replicas.use";
    public static final boolean DEFAULT_USE_META_REPLICAS = false;
    public static final String META_REPLICAS_NUM = "hbase.meta.replica.count";
    public static final int DEFAULT_META_REPLICA_NUM = 1;

    /**
     * The name of the configuration parameter that specifies
     * the number of bytes in a newly created checksum chunk.
     */
    public static final String BYTES_PER_CHECKSUM = "hbase.hstore.bytes.per.checksum";

    /**
     * The name of the configuration parameter that specifies
     * the name of an algorithm that is used to compute checksums
     * for newly created blocks.
     */
    public static final String CHECKSUM_TYPE_NAME = "hbase.hstore.checksum.algorithm";

    /** Enable file permission modification from standard hbase */
    public static final String ENABLE_DATA_FILE_UMASK = "hbase.data.umask.enable";
    /** File permission umask to use when creating hbase data files */
    public static final String DATA_FILE_UMASK_KEY = "hbase.data.umask";

    /** Configuration name of WAL Compression */
    public static final String ENABLE_WAL_COMPRESSION = "hbase.regionserver.wal.enablecompression";

    /** Configuration name of WAL storage policy
     * Valid values are: HOT, COLD, WARM, ALL_SSD, ONE_SSD, LAZY_PERSIST
     * See http://hadoop.apache.org/docs/r2.7.3/hadoop-project-dist/hadoop-hdfs/ArchivalStorage.html*/
    public static final String WAL_STORAGE_POLICY = "hbase.wal.storage.policy";
    /**
     * "NONE" is not a valid storage policy and means we defer the policy to HDFS. @see
     * <a href="https://issues.apache.org/jira/browse/HBASE-20691">HBASE-20691</a>
     */
    public static final String DEFER_TO_HDFS_STORAGE_POLICY = "NONE";
    /** By default we defer the WAL storage policy to HDFS */
    public static final String DEFAULT_WAL_STORAGE_POLICY = DEFER_TO_HDFS_STORAGE_POLICY;

    /** Region in Transition metrics threshold time */
    public static final String METRICS_RIT_STUCK_WARNING_THRESHOLD = "hbase.metrics.rit.stuck.warning.threshold";

    public static final String LOAD_BALANCER_SLOP_KEY = "hbase.regions.slop";

    /** delimiter used between portions of a region name */
    public static final int DELIMITER = ',';

    /**
     * QOS attributes: these attributes are used to demarcate RPC call processing
     * by different set of handlers. For example, HIGH_QOS tagged methods are
     * handled by high priority handlers.
     */
    // normal_QOS < replication_QOS < replay_QOS < QOS_threshold < admin_QOS < high_QOS < meta_QOS
    public static final int PRIORITY_UNSET = -1;
    public static final int NORMAL_QOS = 0;
    public static final int REPLICATION_QOS = 5;
    public static final int REPLAY_QOS = 6;
    public static final int QOS_THRESHOLD = 10;
    public static final int ADMIN_QOS = 100;
    public static final int HIGH_QOS = 200;
    public static final int SYSTEMTABLE_QOS = HIGH_QOS;
    /**
     * @deprecated the name "META_QOS" is a bit ambiguous, actually only meta region transition can
     *             use this priority, and you should not use this directly. Will be removed in 3.0.0.
     */
    @Deprecated
    public static final int META_QOS = 300;

    /** Directory under /hbase where archived hfiles are stored */
    public static final String HFILE_ARCHIVE_DIRECTORY = "archive";

    /**
     * Name of the directory to store all snapshots. See SnapshotDescriptionUtils for
     * remaining snapshot constants; this is here to keep HConstants dependencies at a minimum and
     * uni-directional.
     */
    public static final String SNAPSHOT_DIR_NAME = ".hbase-snapshot";

    /* Name of old snapshot directory. See HBASE-8352 for details on why it needs to be renamed */
    public static final String OLD_SNAPSHOT_DIR_NAME = ".snapshot";

    /** Temporary directory used for table creation and deletion */
    public static final String HBASE_TEMP_DIRECTORY = ".tmp";
    /**
     * The period (in milliseconds) between computing region server point in time metrics
     */
    public static final String REGIONSERVER_METRICS_PERIOD = "hbase.regionserver.metrics.period";
    public static final long DEFAULT_REGIONSERVER_METRICS_PERIOD = 5000;
    /** Directories that are not HBase table directories */
    public static final List<String> HBASE_NON_TABLE_DIRS = Collections
            .unmodifiableList(Arrays.asList(new String[]{HBCK_SIDELINEDIR_NAME, HBASE_TEMP_DIRECTORY, MIGRATION_NAME}));

    /** Directories that are not HBase user table directories */
    public static final List<String> HBASE_NON_USER_TABLE_DIRS = Collections.unmodifiableList(
            Arrays.asList((String[]) ArrayUtils.addAll(new String[]{TableName.META_TABLE_NAME.getNameAsString()}, HBASE_NON_TABLE_DIRS.toArray())));

    /** Health script related settings. */
    public static final String HEALTH_SCRIPT_LOC = "hbase.node.health.script.location";
    public static final String HEALTH_SCRIPT_TIMEOUT = "hbase.node.health.script.timeout";
    public static final String HEALTH_CHORE_WAKE_FREQ = "hbase.node.health.script.frequency";
    public static final long DEFAULT_HEALTH_SCRIPT_TIMEOUT = 60000;
    /**
     * The maximum number of health check failures a server can encounter consecutively.
     */
    public static final String HEALTH_FAILURE_THRESHOLD = "hbase.node.health.failure.threshold";
    public static final int DEFAULT_HEALTH_FAILURE_THRESHOLD = 3;


    /**
     * Setting to activate, or not, the publication of the status by the master. Default
     *  notification is by a multicast message.
     */
    public static final String STATUS_PUBLISHED = "hbase.status.published";
    public static final boolean STATUS_PUBLISHED_DEFAULT = false;

    /**
     * IP to use for the multicast status messages between the master and the clients.
     * The default address is chosen as one among others within the ones suitable for multicast
     * messages.
     */
    public static final String STATUS_MULTICAST_ADDRESS = "hbase.status.multicast.address.ip";
    public static final String DEFAULT_STATUS_MULTICAST_ADDRESS = "226.1.1.3";

    /**
     * The address to use for binding the local socket for receiving multicast. Defaults to
     * 0.0.0.0.
     * @see <a href="https://issues.apache.org/jira/browse/HBASE-9961">HBASE-9961</a>
     */
    public static final String STATUS_MULTICAST_BIND_ADDRESS = "hbase.status.multicast.bind.address.ip";
    public static final String DEFAULT_STATUS_MULTICAST_BIND_ADDRESS = "0.0.0.0";

    /**
     * The port to use for the multicast messages.
     */
    public static final String STATUS_MULTICAST_PORT = "hbase.status.multicast.address.port";
    public static final int DEFAULT_STATUS_MULTICAST_PORT = 16100;

    /**
     * The network interface name to use for the multicast messages.
     */
    public static final String STATUS_MULTICAST_NI_NAME = "hbase.status.multicast.ni.name";

    /**
     * The address to use for binding the local socket for sending multicast. Defaults to 0.0.0.0.
     */
    public static final String STATUS_MULTICAST_PUBLISHER_BIND_ADDRESS = "hbase.status.multicast.publisher.bind.address.ip";
    public static final String DEFAULT_STATUS_MULTICAST_PUBLISHER_BIND_ADDRESS = "0.0.0.0";

    public static final long NO_NONCE = 0;

    /** Default cipher for encryption */
    public static final String CIPHER_AES = "AES";

    /** Configuration key for the crypto algorithm provider, a class name */
    public static final String CRYPTO_CIPHERPROVIDER_CONF_KEY = "hbase.crypto.cipherprovider";

    /** Configuration key for the crypto key provider, a class name */
    public static final String CRYPTO_KEYPROVIDER_CONF_KEY = "hbase.crypto.keyprovider";

    /** Configuration key for the crypto key provider parameters */
    public static final String CRYPTO_KEYPROVIDER_PARAMETERS_KEY = "hbase.crypto.keyprovider.parameters";

    /** Configuration key for the name of the master key for the cluster, a string */
    public static final String CRYPTO_MASTERKEY_NAME_CONF_KEY = "hbase.crypto.master.key.name";

    /** Configuration key for the name of the alternate master key for the cluster, a string */
    public static final String CRYPTO_MASTERKEY_ALTERNATE_NAME_CONF_KEY = "hbase.crypto.master.alternate.key.name";

    /** Configuration key for the algorithm to use when encrypting the WAL, a string */
    public static final String CRYPTO_WAL_ALGORITHM_CONF_KEY = "hbase.crypto.wal.algorithm";

    /** Configuration key for the name of the master WAL encryption key for the cluster, a string */
    public static final String CRYPTO_WAL_KEY_NAME_CONF_KEY = "hbase.crypto.wal.key.name";

    /** Configuration key for the algorithm used for creating jks key, a string */
    public static final String CRYPTO_KEY_ALGORITHM_CONF_KEY = "hbase.crypto.key.algorithm";

    /** Configuration key for the name of the alternate cipher algorithm for the cluster, a string */
    public static final String CRYPTO_ALTERNATE_KEY_ALGORITHM_CONF_KEY = "hbase.crypto.alternate.key.algorithm";

    /** Configuration key for enabling WAL encryption, a boolean */
    public static final String ENABLE_WAL_ENCRYPTION = "hbase.regionserver.wal.encryption";

    /** Configuration key for setting RPC codec class name */
    public static final String RPC_CODEC_CONF_KEY = "hbase.client.rpc.codec";

    /** Configuration key for setting replication codec class name */
    public static final String REPLICATION_CODEC_CONF_KEY = "hbase.replication.rpc.codec";

    /** Maximum number of threads used by the replication source for shipping edits to the sinks */
    public static final String REPLICATION_SOURCE_MAXTHREADS_KEY = "hbase.replication.source.maxthreads";

    /** Drop edits for tables that been deleted from the replication source and target */
    public static final String REPLICATION_DROP_ON_DELETED_TABLE_KEY = "hbase.replication.drop.on.deleted.table";

    /** Maximum number of threads used by the replication source for shipping edits to the sinks */
    public static final int REPLICATION_SOURCE_MAXTHREADS_DEFAULT = 10;

    /** Configuration key for SplitLog manager timeout */
    public static final String HBASE_SPLITLOG_MANAGER_TIMEOUT = "hbase.splitlog.manager.timeout";

    /**
     * Configuration keys for Bucket cache
     */
    // TODO moving these bucket cache implementation specific configs to this level is violation of
    // encapsulation. But as these has to be referred from hbase-common and bucket cache
    // sits in hbase-server, there were no other go! Can we move the cache implementation to
    // hbase-common?

    /**
     * Current ioengine options in include: heap, offheap and file:PATH (where PATH is the path
     * to the file that will host the file-based cache.  See BucketCache#getIOEngineFromName() for
     * list of supported ioengine options.
     * <p>Set this option and a non-zero {@link #BUCKET_CACHE_SIZE_KEY} to enable bucket cache.
     */
    public static final String BUCKET_CACHE_IOENGINE_KEY = "hbase.bucketcache.ioengine";

    /**
     * When using bucket cache, this is a float that EITHER represents a percentage of total heap
     * memory size to give to the cache (if &lt; 1.0) OR, it is the capacity in
     * megabytes of the cache.
     */
    public static final String BUCKET_CACHE_SIZE_KEY = "hbase.bucketcache.size";

    /**
     * HConstants for fast fail on the client side follow
     */
    /**
     * Config for enabling/disabling the fast fail mode.
     */
    public static final String HBASE_CLIENT_FAST_FAIL_MODE_ENABLED = "hbase.client.fast.fail.mode.enabled";

    public static final boolean HBASE_CLIENT_ENABLE_FAST_FAIL_MODE_DEFAULT = false;

    public static final String HBASE_CLIENT_FAST_FAIL_THREASHOLD_MS = "hbase.client.fastfail.threshold";

    public static final long HBASE_CLIENT_FAST_FAIL_THREASHOLD_MS_DEFAULT = 60000;

    public static final String HBASE_CLIENT_FAILURE_MAP_CLEANUP_INTERVAL_MS = "hbase.client.failure.map.cleanup.interval";

    public static final long HBASE_CLIENT_FAILURE_MAP_CLEANUP_INTERVAL_MS_DEFAULT = 600000;

    public static final String HBASE_CLIENT_FAST_FAIL_CLEANUP_MS_DURATION_MS = "hbase.client.fast.fail.cleanup.duration";

    public static final long HBASE_CLIENT_FAST_FAIL_CLEANUP_DURATION_MS_DEFAULT = 600000;

    public static final String HBASE_CLIENT_FAST_FAIL_INTERCEPTOR_IMPL = "hbase.client.fast.fail.interceptor.impl";

    public static final String HBASE_SPLIT_WAL_COORDINATED_BY_ZK = "hbase.split.wal.zk.coordinated";

    public static final boolean DEFAULT_HBASE_SPLIT_COORDINATED_BY_ZK = true;

    public static final String HBASE_SPLIT_WAL_MAX_SPLITTER = "hbase.regionserver.wal.max.splitters";

    public static final int DEFAULT_HBASE_SPLIT_WAL_MAX_SPLITTER = 2;

    /** Config key for if the server should send backpressure and if the client should listen to
     * that backpressure from the server */
    public static final String ENABLE_CLIENT_BACKPRESSURE = "hbase.client.backpressure.enabled";
    public static final boolean DEFAULT_ENABLE_CLIENT_BACKPRESSURE = false;

    public static final String HEAP_OCCUPANCY_LOW_WATERMARK_KEY = "hbase.heap.occupancy.low_water_mark";
    public static final float DEFAULT_HEAP_OCCUPANCY_LOW_WATERMARK = 0.95f;
    public static final String HEAP_OCCUPANCY_HIGH_WATERMARK_KEY = "hbase.heap.occupancy.high_water_mark";
    public static final float DEFAULT_HEAP_OCCUPANCY_HIGH_WATERMARK = 0.98f;

    /**
     * The max number of threads used for splitting storefiles in parallel during
     * the region split process.
     */
    public static final String REGION_SPLIT_THREADS_MAX = "hbase.regionserver.region.split.threads.max";

    /** Canary config keys */
    // TODO: Move these defines to Canary Class
    public static final String HBASE_CANARY_WRITE_DATA_TTL_KEY = "hbase.canary.write.data.ttl";

    public static final String HBASE_CANARY_WRITE_PERSERVER_REGIONS_LOWERLIMIT_KEY = "hbase.canary.write.perserver.regions.lowerLimit";

    public static final String HBASE_CANARY_WRITE_PERSERVER_REGIONS_UPPERLIMIT_KEY = "hbase.canary.write.perserver.regions.upperLimit";

    public static final String HBASE_CANARY_WRITE_VALUE_SIZE_KEY = "hbase.canary.write.value.size";

    public static final String HBASE_CANARY_WRITE_TABLE_CHECK_PERIOD_KEY = "hbase.canary.write.table.check.period";

    public static final String HBASE_CANARY_READ_RAW_SCAN_KEY = "hbase.canary.read.raw.enabled";

    /**
     * Configuration keys for programmatic JAAS configuration for secured ZK interaction
     */
    public static final String ZK_CLIENT_KEYTAB_FILE = "hbase.zookeeper.client.keytab.file";
    public static final String ZK_CLIENT_KERBEROS_PRINCIPAL = "hbase.zookeeper.client.kerberos.principal";
    public static final String ZK_SERVER_KEYTAB_FILE = "hbase.zookeeper.server.keytab.file";
    public static final String ZK_SERVER_KERBEROS_PRINCIPAL = "hbase.zookeeper.server.kerberos.principal";

    /** Config key for hbase temporary directory in hdfs */
    public static final String TEMPORARY_FS_DIRECTORY_KEY = "hbase.fs.tmp.dir";
    public static final String DEFAULT_TEMPORARY_HDFS_DIRECTORY = "/user/" + System.getProperty("user.name") + "/hbase-staging";

    public static final String SNAPSHOT_RESTORE_TAKE_FAILSAFE_SNAPSHOT = "hbase.snapshot.restore.take.failsafe.snapshot";
    public static final boolean DEFAULT_SNAPSHOT_RESTORE_TAKE_FAILSAFE_SNAPSHOT = true;

    public static final String SNAPSHOT_RESTORE_FAILSAFE_NAME = "hbase.snapshot.restore.failsafe.name";
    public static final String DEFAULT_SNAPSHOT_RESTORE_FAILSAFE_NAME = "hbase-failsafe-{snapshot.name}-{restore.timestamp}";

    public static final String DEFAULT_LOSSY_COUNTING_ERROR_RATE = "hbase.util.default.lossycounting.errorrate";
    public static final String NOT_IMPLEMENTED = "Not implemented";

    /**
     * Configurations for master executor services.
     */
    public static final String MASTER_OPEN_REGION_THREADS = "hbase.master.executor.openregion.threads";
    public static final int MASTER_OPEN_REGION_THREADS_DEFAULT = 5;

    public static final String MASTER_CLOSE_REGION_THREADS = "hbase.master.executor.closeregion.threads";
    public static final int MASTER_CLOSE_REGION_THREADS_DEFAULT = 5;

    public static final String MASTER_SERVER_OPERATIONS_THREADS = "hbase.master.executor.serverops.threads";
    public static final int MASTER_SERVER_OPERATIONS_THREADS_DEFAULT = 5;

    public static final String MASTER_META_SERVER_OPERATIONS_THREADS = "hbase.master.executor.meta.serverops.threads";
    public static final int MASTER_META_SERVER_OPERATIONS_THREADS_DEFAULT = 5;

    public static final String MASTER_LOG_REPLAY_OPS_THREADS = "hbase.master.executor.logreplayops.threads";
    public static final int MASTER_LOG_REPLAY_OPS_THREADS_DEFAULT = 10;

    private HConstants() {
        // Can't be instantiated with this ctor.
    }
}
